As a radio communication system between the base station and communication terminals, standards based on the OFDM (Orthogonal Frequency-Division Multiplexing) system such as LTE (Long Term Evolution) and UMB (Ultra Mobile Broadband) are known. In the OFDM system, a frequency band used for a radio communication is separated into a plurality of subbands. The base station, in transmitting data to the communication terminals that are under control of the base station itself, schedules a radio resource by assigning the data for the communication terminals to the subbands. The base station, in order to appropriately schedule, uses CQI (Channel Quality Indicator) reports received from the communication terminals The CQI report is a report of downlink radio quality of the communication terminal provided to the base station. The base station, based on the received CQI report, schedules the transmission data for the radio communication terminal to a frequency band with good radio quality, thereby improving downlink throughput (for example, see Non-Patent Documents 1, 2 listed below).
There are a variety of formats of the CQI report transmitted from the communication terminal to the base station. For example, the CQI report includes average radio quality of an entire frequency band, an average radio quality of each of the subbands and the like. A data size of the CQI report varies based on a CQI report format.
For example, when the CQI report includes the average radio quality of the entire frequency band alone, the data size of the CQI report is small, thus consumption of an uplink radio resource may be reduced. In this case, while an information quantity processed by the base station is small, the base station is not able to obtain the radio quality of each of the subbands from the average radio quality of the entire frequency band alone. Therefore, the base station may not be able to assign the communication terminal to the subband having good radio quality, failing to schedule for efficient use of the frequency.
Also, for example, when the CQI report includes the average radio quality of each of the subbands as well as the average radio quality of the entire frequency band, the data size of the CQI report becomes large, increasing consumption of the uplink radio resource. In this case, although the information quantity processed by the radio base station is increased, the base station may obtain the average radio quality of each of all subbands. Therefore, the base station may assign the communication terminal to the subband having good radio quality, enabling scheduling for efficient use of the frequency.
Non-Patent Document 1: 3GPP TS36.300 “11.5 CQI reporting for scheduling” Non-Patent Document 2: 3GPP TS36.213 “7.2 UE procedure for reporting channel quality indication (CQI), precoding matrix indicator (PMI) and rank indication (RI)”